Really? I may have to investigate this George Whitehead then to see who he is. He only appears with them in 1851 (aged 12). I cannot find Isaac and Mary Ann is 1841 so I can't say if he was with them before.
Any help with a baptism for Isaac would be a big help!
I found 2 Isaac Stanley's on FamilySearch.org who were baptised in Warwickshire in 1810/11. The most promising one is this one;
Isaac Stanley
Baptised 29th Dec 1811, Honily, Warwickshire
Father - Matthew Stanley
Mother - Elizabeth
(Parents living in Wroxall)
This one is most promising for 2 reasons. First, Wroxall and Honiley are only 5 miles from Knowle (where Isaac claims he was born in the 1851 census). Secondly, his father's name is Matthew and Isaac had a son called Matthew. I know that names were often passed down though the generations.